Various methods and compositions for reducing the NO.sub.x concentration in the effluent from the combustion of a carbonaceous fuel have been proposed. For instance, Arand et al, in U.S. Pat. No. 4,208,386, disclose a method for reducing NO.sub.x in combustion effluents by injecting urea, either as a solid powder or in solution, at effluent temperatures in excess of 1300.degree. F. The preferred urea solutions are those having at least 10 weight percent urea. For operation at temperatures below 1600.degree. F., the use of reducing materials such as paraffinic, olefinic, aromatic and oxygenated hydrocarbons, as well as hydrogen, are required.
Similarly, Lyon, in U.S. Pat. No. 3,900,554, discloses the introduction of ammonia, as a pure substance or in the form of ammonium formate, ammonium oxalate or ammonium carbonate, into effluents at temperatures between 1300.degree. F. and 2000.degree. F. For operation at temperatures below 1600.degree. F., the use of reducing materials, as is the case with Arand et al., such as paraffinic, olefinic, aromatic and oxygenated hydrocarbons, as well as carbon monoxide and hydrogen, are required.
Although the prior art processes for reducing nitrogen oxides concentrations are generally effective, there exists a present need for a process which elicits still further NO.sub.x reductions in an economical and convenient manner.